There is a very popular type of watercraft known as a “personal watercraft” which is designed to be operated primarily by a single rider. Although this type of watercraft is commonly employed for single riders, frequently provisions are made for accommodating additional passengers although the maximum number of passengers is more limited than conventional types of watercraft.
This type of watercraft is also generally quite sporting in nature and normally accommodates at least the rider on a type of seat in which the rider sits in a straddle fashion. The passenger's area is frequently open through the rear of the watercraft so as to facilitate entry and exit of the rider and passengers to the body of water in which the watercraft is operating, as this type of watercraft is normally ridden with passengers that are wearing swimming suits.
These personal watercraft are generally quite small so that they can be conveniently transported from the owner's home to a body of water for its use. Because of the small size, the layout of the components is extremely critical, and this gives rise to several design considerations that are peculiar to this type of watercraft. However, due to its sporting nature it is also desirable if the watercraft is powered by an engine and propulsion device that are not only efficient but also generate sufficient power.
Traditionally, two-cycle engines have been used to power watercraft, including personal watercraft. These engines have the advantage that they are fairly powerful, relatively lightweight, and compact.
One particular disadvantage to the two-cycle engine is its emission content. Two-cycle engines generally exhaust larger quantities of hydrocarbons and other pollutants than four-cycle engines due to cylinder charging inefficiencies and the combustion of lubricating oil among other things. When measures are taken to reduce emissions of the two-cycle engine, other generally undesirable consequences can result, such as an increase in the weight of the engine, a reduction of its power output or the like. With concern for the environment and increasingly strict emissions requirements being instituted by various governing bodies. There is motivation to provide a power plant that reduces exhaust emissions while retaining other advantageous characteristics such as compactness, low weight and high power output.
Four-cycle engines are commonly used as power plants in other applications, such as automobiles. These engines have the advantage that their emissions output are generally desirably lower as compared to a two-cycle engine for a given power output. These engines are typically larger than two-cycle engines and present numerous spatial issues when located in a personal watercraft.
Superchargers are used to enhance engine performance. To date, the present inventors are not aware of the use of a supercharger in an engine for a personal watercraft. U.S. Pat. No. 5,634,422 to Kobayashi et al., entitled “Personal Watercraft With V-Type Engine,” U.S. Pat. No. 5,647,779 to Nanami, entitled “Manifold and Water Trap System For A Marine Engine,” U.S. Pat. No. 5,839,930 to Nanami et al., entitled “Engine Lubricating System For Watercraft,” and U.S. Pat. No. 5,846,102 to Nitta et al., entitled “Four-Cycle Engine For A Small Jet Boat” disclose various engines for personal watercraft. None of these references disclose the use of a supercharger.